I was fiddling around & ended up sorta recreating a Shepard Tone (in Auxy, of course). If you don’t know what a Shepard Tone is, you can read about it here. Apparently a true Shepard tone uses sine waves, so this may not be pure, but it has the same illusion. As for production, I filled a 1-bar pattern with 32nd notes, duplicated the instrument, and did some automation:

First pattern:

Pitch -100% to 0%

Volume 0% to 100%

Second pattern:

Pitch 0% to 100%

Volume 100% to 0%

Ran into some problems because Auxy’s volume automation isn’t linear, so I slightly adjusted the volume automation (made a fake curve) to fit.